1. Field of the Invention
The present invention relates to an apparatus and method for improving error control in a communication system. More particularly, the present invention relates to an apparatus and method for transmitting and receiving an Automatic Retransmission reQuest (ARQ) feedback Information Element (IE) in a communication system.
2. Description of the Related Art
The next-generation communication system is being developed to provide various high-speed, high-capacity services to Mobile Stations (MSs). Examples of the next-generation communication system include an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system and a Mobile Worldwide Interoperability for Microwave Access (WiMAX) communication system. In a communication system, the efficiency and reliability of transmitting and receiving signals over a channel are important factors when considering the performance of the communication system. However, when transmitting and receiving signals, the communication system may inevitably suffer an error due to noise, interference and/or fading according to the channel condition. Thus, the communication system uses an error control scheme to reduce an information loss caused by such an error. A typical error control scheme can include an ARQ scheme, which is used by the IEEE 802.16 communication system.
A description will now be made of four ARQ feedback Information Element (IE) types used in the IEEE 802.16 communication system.
The first ARQ feedback IE type is a type for indicating success/failure in normal reception of each ARQ data block beginning from an ARQ data block corresponding to an arbitrary Block Sequence Number (BSN), using the arbitrary BSN and each bit of an Acknowledgement (ACK) MAP. For convenience, the first ARQ feedback IE type will be called a ‘selective ACK type’.
The second ARQ feedback IE type is a type for indicating only the BSN of an ARQ data block that is first abnormally received or not received, i.e., for which Negative Acknowledgement (NAK) block should first be subject to feedback. Here, the NAK block denotes a block indicating NAK information. For convenience, the second ARQ feedback IE type will be called a ‘cumulative ACK type’. The use of the cumulative ACK type indicates success in normal reception of an ARQ data block corresponding to all BSNs preceding the BSN included in an ARQ feedback IE.
The third ARQ feedback IE type is a type for indicating success/failure in normal reception of each ARQ data block, using a BSN of an ARQ data block that is first abnormally received or not received, i.e., for which NAK block should first be subject to feedback, and each bit of an ACK MAP beginning from an ARQ data block corresponding to a BSN, for which NAK block should first be subject to feedback. For convenience, the third ARQ feedback IE type will be called a ‘cumulative ACK+ bitmap ACK type’.
The fourth ARQ feedback IE type is a type for indicating the number of consecutive ACK/NAK blocks using a BSN of an ARQ data block that is first abnormally received or not received, i.e., for which NAK block should first be subject to feedback, and a block sequence MAP. For convenience, the fourth ARQ feedback IE type will be called a ‘cumulative ACK+ sequence MAP ACK type’.
With reference to FIG. 1, a description will now be made of an ARQ feedback IE format used for transmitting an ARQ feedback IE in an IEEE 802.16 communication system.
FIG. 1 is a diagram illustrating an ARQ feedback IE format for a conventional IEEE 802.16 communication system.
Referring to FIG. 1, the ARQ feedback IE includes a Connection IDentifier (CID) field 111, a LAST field 113, an ACK type field 115, a BSN field 117, a ‘Number of ACK MAPs’ field 119, and a plurality of, for example, four ACK MAP fields 121, 123, 125 and 127.
The CID field 111 is a field indicating a CID of a corresponding ARQ connection, and the CID field 111 is expressed with 16 bits. The CID can be assigned to each MS individually, or can be individually assigned to each service flow having a different Quality-of-service (QoS) at the same MS. When the CID is individually assigned to each service flow having a different QoS at the same MS, a plurality of CIDs can be assigned to one MS. The LAST field 113 indicates the presence/absence of another ARQ feedback IE after the current ARQ feedback IE, and the LAST field 113 is realized with 1 bit. For example, when the corresponding 1 bit of the LAST field 113 has a value ‘1’, it indicates the absence of another ARQ feedback IE after the current ARQ feedback IE. On the contrary, if the 1 bit of the LAST field 113 has a value ‘0’, it indicates the presence of another ARQ feedback IE after the current ARQ feedback IE. The ACK type field 115 is a field indicating an ARQ feedback IE type, and is expressed with 2 bits. That is, the 2 bits of the ACK type field 115 are used to indicate which of the above described four types of ARQ feedback IE is being used.
In addition, the BSN field 117 indicates a BSN, and is realized with 11 bits. The BSN indicated by the BSN field 117 is determined according to the ARQ feedback IE type. The ‘Number of ACK MAPs’ field 119 indicates the number of ACK MAPs included in the ARQ feedback IE and is realized with 2 bits. The ACK MAP fields 121, 123, 125 and 127 each indicate an ARQ MAP and are each realized with 16 bits. The ARQ MAP is a bitmap indicating success/failure in normal reception of an ARQ data block including an ARQ data block corresponding to a particular BSN. For example, when a corresponding bit has a value ‘1’, it indicates that the corresponding ARQ data block is normally received. On the contrary, if the corresponding bit has a value ‘0’, it indicates that the corresponding ARQ data block is not normally received, or never received.
The ARQ feedback IE is used by an ARQ data block reception apparatus to comprehensively notify an ARQ data block transmission apparatus of success/failure in normal reception of all received ARQ data blocks. However, as described in FIG. 1, in the IEEE 802.16 communication system, the number of ACK MAPs that may be included in one ARQ feedback IE is limited to four. Therefore, when the amount of ARQ data blocks that the ARQ data block reception apparatus has received is greater than the amount that may be expressed with the limited number of ACK MAPs, it is difficult to comprehensively notify the ARQ data block transmission apparatus of success/failure in normal reception of all ARQ data blocks. Of course, when the selective ACK type is used, since the BSN included in the ARQ feedback IE is an arbitrary BSN, it is possible for the ARQ data block reception apparatus to transmit more than four ACK MAPs by transmitting multiple ARQ feedback IEs. However, it is inefficient that the selective ACK type should indicate success/failure in normal reception for each of all ARQ data blocks, using bits. Therefore, the current IEEE 802.16 communication system tends to use the cumulative ACK type as the ARQ feedback IE type, avoiding use of the selective ACK type. Thus, the current IEEE 802.16 communication system tends to use the ARQ feedback IE type based on the cumulative ACK type, i.e., uses the cumulative ACK type, the cumulative ACK+ bitmap ACK type, and the cumulative ACK+ sequence MAP ACK type.
However, regarding the cumulative ACK type, since the BSN included in an ARQ feedback IE always indicates only the BSN of an ARQ data block, which is first abnormally received or not received, i.e., for which NAK block should first be subject to feedback, it is not possible for the ARQ data block reception apparatus to transmit a plurality of consecutive ARQ feedback IEs for one CID. Since it is not possible for the ARQ data block reception apparatus to transmit a plurality of ARQ feedback IEs, the number of ACK MAPs transmittable by the ARQ data block reception apparatus is always limited to four. When a traffic rate of a single ARQ connection is high and a transmission period of the ARQ feedback IE is long, it is impossible for the ARQ data block reception apparatus to transmit in one ARQ feedback IE the success/failure in normal reception for all received ARQ data blocks due to the above-stated limitation on the number of ACK MAPs. In this case, the traffic rate may be reduced due to the transmission of the ARQ feedback IE. Therefore, even though there are sufficient wireless resources, the ARQ-based process may be delayed, causing a reduction in the entire system performance.